Tire / Speed Question

The outside diameter of the two tire sizes is different, the 17" tire being the smaller of the two. It will do roughly 3% more revolutions in any given distance travelled.

I try to think about how that applies,... but nothing happens: the coffee's worn off. Perhaps someone more on the ball can take over

 

The 215/45/17 should be very close in overall rolling diameter to your stock 185/65/15s and therefore should not affect your MPH attainable in EV mode. My guess is the extra weight and friction from the new 17s are requiring more HP to turn and therefore causing EV mode to cut out early. This is just speculation and I doubt this is really the case. Most likely the cause is something to due with the incline/surface in which you are performing this test and or weather and operating conditions of the vehicle.

 

Here is a comparison between both sizes of tires:

Tire Size Comparison
Specification Sidewall Radius Diameter Circumference Revs/Mile Difference
185/65-15 4.7in 12.2in 24.5in 76.9in 824 0.0%
215/45-17 3.8in 12.3in 24.6in 77.3in 819 0.6%
or

Punch the tire sizes into this calculator and you will come up with nearly the exact same results

http://www.1010tires.com/tiresizecalculator.asp

 

The stock 15" tire on 2010 is 195/65R15, so there is more signif. difference. My calc:

195/65R15 tire height: 126.75mm (195 * 0.65)
215/45R17 tire height: 96.75mm (215 * 0.45)

195/65R15 tire circumference: 1993.3405mm (78.4780")
215/45R17 tire circumference: 1964.4379mm (77.3401")

17" circumference divided by 15" circumference: 0.9855

15" circumference divided by 17" circumference: 1.0147

So, the 17", with it's smaller OD, yields about 1.5% more rev's per given distance. Less than my first posting

 

Uggg, that's what I get for not noticing I was still in the GenIII forum. lol

That being said, we are still only talking about a 1.5mph (too fast) difference between the two.

 

No problem. Still can't get my head around what that does for the OP's EV cut-off, though. Ok: say with stock tires the car thinks it's going 18 mph. Now put on the smaller od 17" tires, when the odometer reads 18mph it's actually going... slower, say if you read it's speed with a radar gun. Due to the smaller wheels having to spin faster. Maybe it all cancels out, well as far as the car is concerned?

 

I agree. That is why I don't think the issue has anything to do with the difference in diameter and more to do with environmental and/or vehicle conditions or the HP required to overcome the weight and friction of the new combo. Or there just has not been enough testing performed by the OP to determine that this happens exclusively after the wheel/tire change.

 

Like F8L alluded to, I think the issue that the OP is referencing could be related to the additional weight and friction created by the 17s. The OP doesn't mention what type of rim and tire he swapped his 15s with, but assuming they are heavier, this could lead to the ICE kicking in earlier at the 13-15 MPH zone. When I had the OEM 17s on mine, I notice that I would have to engage the ICE sooner during normal acceleration.

 

But, but, but.... the EV mode cuts off at a fixed measured mph. Why would it change with a different diameter tire? The computer should control the EV mode based on the speed that the speedometer says the car is going.

 

It also cuts off as more HP is asked for which is what happens when you want to accelerate at a particular rate but have now added more mass and friction.

Tire diameter will affect the speedometer so why would it not affect the EV cutoff rate if the size difference were large enough?

 

Don't forget that tire weight and rolling resistance plays a large factor as well. Not all tires are created equal.

 

Yeah, tires do make quite a difference. The good thing is, there's a range of LRR tires out now, so you have a few choices to pick from.

 

My V definitely goes higher than 17mph in ev mode.